The present invention generally relates to optical communication devices and, in particular, to variably configurable optical waveguide devices (VOWD).
Optical telecommunication networks over large distances include a wide variety of devices for routing, splitting, interconnecting, modulating and amplifying electromagnetic radiation at optical frequencies, i.e. light. Planar devices such as connectors, switches, power attenuators, beam steerers, directional couplers and intensity modulators, etc., incorporate passive and/or active optical waveguides as basic transport means for an encoded light wave.
There are a variety of passive and (electro-optically) active waveguide structures. Waveguides used at optical frequencies are typically dielectric waveguides, structures in which a dielectric material with high relative permeability μr, and thus high index of refraction n, is surrounded by a material with lower relative permeability μr, i.e. lower index of refraction n. The refractive index or index of refractionn=√{square root over (εrμr)}  (1)
of a medium is a measure of how much the speed of light is reduced inside the medium, wherein εr is the medium's relative permittivity, and μr is its relative permeability.
A waveguide structure guides optical waves by total internal reflection. The most common optical waveguide is optical fiber. However, other types of optical waveguides may also be used, including, e.g., photonic-crystal fibers, which guide waves by any of several distinct mechanisms. The common principle of the different types of optical waveguides is to induce a higher refractive index n in a certain material region (called core layer or region in the sequel) which, when embedded in a region of lower refractive index (called buffer or cladding region in the sequel), acquires waveguiding properties. A refractive index difference and a geometry of a region with different refractive indexes determine the propagation properties of the optical guided wave. For waveguide structures induced in electro-optic materials, the refractive index difference is induced by locally changing an applied electric field according to an electro-optic effect.
The electro-optic effect is a change in the optical properties of a material in response to an electric field that varies slowly compared to the frequency of light. The term electro-optic effect encompasses a number of distinct phenomena, which may be subdivided into change of absorption and/or change of the refractive index. For designing electro-optic optical waveguides the change of the refractive index is of particular interest. This change of the refractive index may be due to the so-called Pockels effect (or linear electro-optic effect) or the so-called Kerr effect (or quadratic electro-optic effect). The Pockels effect describes a change in the refractive index linearly proportional to the applied electric field. The Kerr effect describes a change in the refractive index proportional to the square of the electric field. Whereas only certain crystalline solids show the Pockels effect, all materials display the Kerr effect, with varying magnitudes, but it is generally much weaker than the Pockels effect.
Electro-optic waveguides may be made from inorganic and/or organic materials, such as, e.g., lithium niobate, barium titanate, gallium arsenide, various oxides and ceramics. Alternatively, electro-optic polymer based waveguide devices can provide cost-effective and high performance devices considering their small velocity mismatch, low optical loss and the possibility of operation at high speed. Further, there are various blends and composites of organic and/or inorganic materials, known by the skilled person, which are used in existing devices or are still in research for waveguide devices.
Generally, waveguide structures are fabricated by methods such as coating methods in interplay with patterning methods, such as photolithography (photochemical structuring), mechanical structuring via hot embossing, replication and other imprint methods, diffusion as well as implantation of molecules, atoms or ions, UV-reactive processes, whereas a refractive index variation of polymers may be induced by varying the irradiation time and intensity.
A drawback of conventional waveguide devices and methods for their fabrication is that once the waveguide materials are structured, their geometry cannot be changed anymore.